Hamato Ben: Omni Mutant
by SaurusRock625
Summary: When Ben is kicked out of the Plumbers, he runs away to New York city. With Kraang, mutants, and ninjas all around him, what could possibly go wrong?
1. Chapter 1

_**This idea has been stuck in my head for the longest time now! A Ben 10 TMNT Crossover! This one is with the current Teenage Mutant Ninja Turtles shown on Nickelodeon, but I do plan for Ben to be mutated later on in the story. I just haven't decided on what kind of animal I should use. But I do have a few ideas for what Danny's weapon should be. He won't just be relying on the Omnitrix in this story, so he'll have more versatility.**_

 _ **Pairing: Ben T. x Karai**_

 _ **Disclaimer: I don't own Ben 10, or Teenage Mutant Ninja Turtles!**_

* * *

"Normal Speech"

 _"Thoughts"_

 _Songs_

 **"Yelling"**

 **Alien Database**

* * *

 _ **Prologue: Terraspin vs. Razar!**_

* * *

In the streets of New York City, a lone teenage boy was walking through the streets with a depressed look in his eyes. He was wearing a black and green shirt, khaki cargo pants, and a pair of white and green sneakers. He had lightly tanned skin, messy brown hair, and green eyes. He was also wearing a sleek wristwatch with a square faceplate that was black with green buttons, and a green hourglass design. This is Ben Tennyson, former hero of Bellwood.

Now many of you may be wondering why I said former hero. Well, he decided to quit the hero gig after he was kicked out of an intergalactic police force calling themselves the Plumbers for no reason. And to make matters worse, his parents kicked him out of the house and practically abandoned him!

In response to this, Ben turned into an alien transformation that he calls Jetray, and flew out of Bellwood as fast as his wings could take him! In his anger and sadness, Ben flew for what felt like days but in reality was hours. Finally, he had landed in New York and turned back to normal. So here he was, walking around in the alleys of the city with nowhere to go, and no family to turn to.

As Ben walked along the path between two buildings, he couldn't shake the feeling that someone was watching him. And he would be right, as a pair of glowing red eyes was watching his every move. Ben stopped when he heard animalistic growling coming from the trash cans behind him.

He turned around thinking that it was a stray dog looking for a good meal, but what he saw almost made him go into a panic. It looked like a cross between a human and a wolf with glowing red eyes. It was clearly male, and had a build that was almost skeletal. He stood on his hind legs, had no tail, and was covered in dark brown fur that was almost black.

"Well, well, well. If it isn't the famous Ben Tennyson. Why would you be here in New York?" asked the mystery wolf.

"Don't call me Tennyson! I'm no longer a Tennyson, nor am I a Plumber!" Ben said.

The wolf thing seemed to chuckle maliciously as he got into a battle stance. Ben activated the Omnitrix, and a green wheel appeared. The wheel had the faces of his aliens on it, and spun until it stopped on the face of a humanoid dinosaur. He lifted his fingers, and the faceplate slid open to reveal the core.

"What's your name anyway?" Ben asked. "I like to know the names of the people I'm fighting."

"My name was once Chris Bradford. But you may call me... Razar!"

"Well then Razar, let's see you take on Humungousaur!" Ben said.

He slammed his hand on the Omnitrix core, and transformed into an alien. However, it wasn't the one that Ben was hoping for. Ben turned into an alien that looked like a cross between a sea turtle, and a tortoise. Its head was mostly in its shell, his arms were replaced by huge flippers that were the same as those found on sea turtles, and his legs were like those of a tortoise. He was mostly green with a yellow and brown shell that had six big holes in the front of the torso area.

"Terraspin?!" Ben said in a gloomy voice. "Great. I'll turtle him into submission!"

* * *

 **Alien Database Entry**

 **Species Name: Geochelone Aerio**

 **Given Name: Terraspin**

 **A near extinct species of alien that is similar to turtles. However, these guys are a lot stronger than they look. By retracting their head into their shell and merging their legs into a third flipper, they can spin like a giant fan to release gusts of gale force winds to literally blow away the competition! And like regular turtles, Geochelone Aerio's are capable of retracting their heads and limbs into their shells for extra defense, and house a set of retractable claws in their flippers!**

 **But wait, there's more! Geochelone Aerio are also capable of using miniscule amounts of magic. This in turn makes them invulnerable to an Anodite's mana based attacks! They can also release tornado force winds from the holes in the front of their shells, making it real tough for enemies to get in close for an attack.**

 **Yet despite these awesome powers, the Geochelone Aerio are not invincible. They are a pacifistic race, and prefer to settle their disputes with diplomacy rather than actual violence. They are also not very fast when running, and can also be corrupted if they absorb too much magical power.**

* * *

Razar didn't know what this form could do, but he had to be careful. One wrong move, and he could be defeated faster than he could blink. And it seems like Terraspin was about to make the first move! Three claws shot out of each flipper, and the turtle alien charged at Razar.

But the wolf mutant was more than prepared to handle hand-to-hand combat! He countered Terraspin's strikes with a few jabs, chops, punches, and kicks of his own. The two kept at this until they ended up outside of the alley.

That was when things went downhill for the canine mutant. With more room, Terraspin was able to use his aerokinesis abilities to the fullest, and use them he did! He retracted his head into his shell, merged his legs into a third flipper, and began to spin them like the blades of a giant fan!

This caused gale force winds to kick up, and made Razar lose his footing. The dog alien almost went flying away, but he managed to hold onto the ground with his clawed hands.

"Grrr! YOU... WON'T... BEAT ME!" Razar declared.

He tried using his claws like hooks to pull himself closer to his enemy, but the winds were growing ever stronger. Razar couldn't hold on any longer, and ended up getting blown away to the farthest part of New York! The Omnitrix started to beep, and in a flash of green Terraspin turned back into Ben.

Unfortunately, it had been so long since Ben had used Terraspin's wind powers to such a degree that he ended up passing out in the street. But it wasn't long before five figures surrounded him, and one of them reached out to Ben as the screen faded to black.

* * *

 _ **There's the prologue for you guys! I hope you all like this story idea, because I really think that this story could go big! Now in case you guys are wondering, this story takes place shortly after the turtles rescue Karai. Anyways, if you have any ideas for a kind of ninja weapon Ben should have, feel free to let me know what it is in the reviews! Thanks, and enjoy!**_


	2. Chapter 2

_**Here's the new chapter of Hamato Ben: Omni Mutant! This chapter is gonna be where the Ben x Karai pairing begins, but it also happens to be where something else happens to Ben. Now I put a lot of work into this chapter, so I hope you guys enjoy it! Also, I just want you to know that the rest of the gang in the Plumbers like Gwen, Kevin, and Maxwell Tennyson all have their Omniverse designs. So I won't be describing them. Now to begin this story, I have just one thing to say. ...BOOYAKASHA!**_

 _ **Disclaimer: I still don't own Ben 10, or Teenage Mutant Ninja Turtles 2012!**_

"Normal Speech"

 _"Thoughts"_

 **"Yelling"**

 **Alien Database**

* * *

All was quiet that night in Bellwood. Its citizens were all asleep without a care in the world. Well, all but one. A Revonnahgander by the name of Rook Blonko had just gotten into Gwen's room where the redhead was asleep with her thumb in her mouth. Rook didn't notice this, and attempted to wake Gwen up.

"Gwen! Hey, Gwen! Wake up!" Rook whispered.

Gwen woke up with a start as her thumb left her mouth with a loud pop. That was when Rook noticed what she was doing in her sleep.

"You suck your thumb?" Rook asked, mildly disturbed.

Gwen sighed as she whipped her drool away, and reached for her glasses that were on the nightstand.

"What is it, Rook? Is there an alien problem?" Gwen asked tiredly. "If it is, then why don't you and Ben go take care of it?"

"That is what I am here about! Ben is not in Bellwood! He is gone!" Rook explained.

"Gone?! WHOA!" Gwen yelped as she fell out of bed. "Whaddya mean gone?"

"I will explain on the way. Right now, I need to go and find Kevin and Magister Tennyson!" Rook said.

With his work there done, Rook jumped out the window and ran to his Proto Truck. He drove off to get Kevin and Max, hoping that they could find Ben before he did anything foolish. Gwen meanwhile decided to get dressed so she could meet up with the others, and try to find her cousin in time.

"Ben... Where are you? Why would you leave like this?" Gwen asked herself.

Oh, if only she knew what was going down with Ben right now in New York. No doubt she'd probably have a heart attack.

* * *

 _Instrumental Opening_

 _Teenage Mutant Ninja Turtles! Teenage Mutant Ninja Turtles! Teenage Mutant Ninja Turtles!_

 _Heroes in a half shell, turtle power!_

 _Here we go it's a lean, green ninja team, On the scene cool teens doin' ninja things!_

 _So extreme out the sewer like laser beams! Get rocked with the shell-shocked pizza kings!_

 _Can't stop these radical dudes! The secret of the ooze made the chosen few,_

 _Emerge from the shadows to make their move! The good guys win, and the bad guys lose!_

 _Interlude_

 _Leonardo's the leader in blue, does anything it takes to get his ninjas through!_

 _Donatello is the fellow has a way with machines!_

 _Raphael's got the most attitude on the team!_

 _MICHAELANGELO! He's one of a kind, and ya know just where to find him when it's party time!_

 _Master Splinter taught them every single skill they'd need to be one lean, mean, green, incredible team!_

 _Teenage Mutant Ninja Turtles! Teenage Mutant Ninja Turtles! Teenage Mutant Ninja Turtles!_

 _Heroes in a half shell,_ _ **TURTLE POWER!**_

* * *

 _ **Meeting the Ninja Turtles!**_

* * *

"How long has Ben been working on this?" Rook asked as he peered down a gopher hole.

He had just gotten Gwen, Kevin, and Max to Ben's house to try and find any trace of Ben, but so far their search had turned up empty. And it didn't help that Rook's tracking skills were worse than a sick Vupimancer's.

"Ben? Ben?!" Rook called into the gopher hole.

"He wouldn't fit down there!" Kevin said in irritation.

Meanwhile, Gwen was literally tossing around her cousin's dirty laundry to try and find her cousin. She was worried as heck for him, and wanted to find him as soon as possible.

"Ben?! Ben?! BEN?!" Gwen called in a worried voice.

"This is crazy! If Ben ran away, where would he even go?!" Max asked.

* * *

 _ *****With Ben*****_

* * *

Ben groaned as he woke up. He didn't know just how long he'd been sleeping, but he had a pretty decent idea as to where he was in the sewers. He slowly opened his eyes so they could adjust to the light. When his vision cleared, Ben noticed that he wasn't in just any sewer.

The room looked a lot like one would expect if they were in their own living room. There was a couch that he was apparently sleeping on, an old looking TV with a wire clothes hanger for an antenna, a videogame system, even a shelf with a few books. Ben guessed that someone must've been living down here, and brought him to their home after his fight with Razar. But the question is... Who brought him here in the first place?

"Where am I? How'd I get here?" Ben asked himself.

He sat up which caused a damp cloth to fall from his forehead to his lap. Ben also felt a serious pain in his chest area, and winced from the pain.

"Dudes, he's awake!" called a voice.

Ben looked over to where he heard the voice came from, and was mildly shocked from what he was seeing. Standing right in front of him were four giant turtles, along with three humans and a giant rat.

The first of the turtles looked like he was the oldest of the four. He had green skin, and a masculine build like that of a warrior. His shell was yellow in the front, and brown in the back, and he was carrying twin katana blades on his back. He was wearing brown wrappings on his feet, white wrappings on his hands, knee and elbow guards, and a blue bandana with eye holes over his eyes.

The other three looked similar to the first, but there were some key differences. One of them was tall and lanky with a purple mask, a gap in his top front teeth, and a bo-staff, another was more muscular with skin that was more of a darker green along with twin sais and a red mask, and the last one seemed to be the youngest with a pair of nunchucks and an orange mask.

The rat was tall with a really long and thin beard, brown and white fur that seemed to be graying somewhat, and brown eyes. He was wearing what appeared to be a Japanese men's battle kimono that was a burgundy color with black trim on the sleeves and collar, and a black sash holding it closed.

The first of the humans was a girl that looked to be about sixteen. She had reddish-orange hair that was pulled into a low ponytail, green eyes, and tan skin. She was wearing a yellow shirt, a pair of jean shorts with black tights underneath, and a pair of gray boots.

The next human was a teenage boy that seemed to be the definition of juvenile delinquent. He was wearing a set of hockey gear, along with a hockey mask that was painted to look like a skull's face. Strapped to his back was a baseball bat, and two hockey sticks. He had short, greasy black hair, pale skin, and a few front teeth were missing. More than likely from taking one too many hockey pucks to the face.

But it was the third teen that really got Ben's attention. It was another girl that looked like she was about Ben's age. She had a darker tan than the first girl, a slender yet feminine frame, and her hair was mostly black with the hair in the back being blonde. She had yellow colored eyes with red eyeliner on the tips of her eyebrows, and was also wearing red lipstick. She was wearing a formfitting black ninja outfit with silver armor on the abdomen, forearms, and shins, along with spiked silver shoes. Ben didn't understand why, but his heart began to beat slightly faster as he gazed into her eyes.

"You have awoken, young one. That is most fortunate." said the rat.

"Yeah, man. Not a lot of people can fight against Razar on even grounds. And then you just literally blow him away!" said the turtle with the red mask.

"THAT WAS AWESOME, DUDE!" said the orange masked turtle.

Ben was still pretty cautious around these guys. Sure they didn't seem hostile, but their weapons put him on edge. The turtle with the blue mask seemed to notice this, and decided to break the ice.

"I'm sorry, where are our manners? My name is Leonardo Hamato, and these are my brothers Donatello, Raphael, and Michelangelo." he said while gesturing to the purple masked, red masked, and orange masked turtles.

Each turtle bowed in greeting, and Ben returned the gesture out of respect. The first two teens walked up and introduced themselves next.

"Hi, I'm April O'Neil. Nice to meet you."

"And I'm Casey Jones, vigilante extraordinaire! At your service!"

Ben shook hands with both of them, and the rat man walked up next. He bowed in greeting, and Ben returned the gesture.

"Greetings, youngling. I am Hamato Yoshi. But you may call me Splinter."

Finally, the black and blonde haired girl walked up. She also bowed in greeting, and Ben once again returned the gesture in an attempt to be respectful.

"My name is Karai."

"It's very good to meet you all. My name's Ben. Formerly, Ben Tennyson."

* * *

 _ **That's all I've got for now. I'm afraid I will have to wait until next chapter to do the mutation and the start of the Ben x Karai relationship. I'm still accepting ideas for Ben's mutant form, and you can even use DNA from the Omnitrix for it if you want to.**_


	3. Chapter 3

_**It's been awhile, hasn't it? Well, I'm back with another chapter for your further enjoyment! But after many weapon ideas and mutant form ideas, I've decided on what Ben will mutate into. However, I'm gonna set up a poll for the weapon. Now it'll be up until next chapter, so be sure to vote!**_

 _ **Disclaimer: I still don't own Ben 10, or Teenage Mutant Ninja Turtles 2012!**_

* * *

"..." = Talking

 _"Italics" = Thinking_

 **"Bold" = Yelling**

* * *

 _ **Mutations and Shredder Part 1!**_

* * *

It's been a few weeks since Ben met Leonardo and the others, and he's fully healed from those injuries he suffered in his fight against Razar. Since then, he's been learning a lot about the turtles and their past. Especially since learning about the Shredder and his vendetta against Splinter.

Ben thought that the fighting styles and weapons these guys used were very impressive. Way more impressive and practical than the stuff that was ever used by the Plumbers. And they didn't have to rely on something like the Omnitrix to fight in their battles! That made Leo and his brothers pretty good warriors in Ben's book.

Ben has watched the four brothers spar in ninjitsu many times before, and was a little jealous. He's always relied on the Omnitrix to fight his battles, but these guys didn't have to worry about timing out and being helpless in a fight.

And as Ben was watching Leo, Donnie, Raph, and Mikey spar against each other, Splinter seemed to notice Ben's jealousy.

"Does something trouble you, Benjamin?" Splinter asked.

Ben sighed. He should've known that he couldn't hide anything from a master ninja.

"I just feel like I'm severely lacking in many areas when it comes to actual combat, Splinter." Ben said. "Looking at your sons, your daughter, and even April, I've realized that I've come to rely on the Omnitrix too much! I need to train myself to get stronger!"

Splinter hummed in understanding. His sons once had the same problem, depending on one type of weapon to win in a fight. Fortunately, they learned how to turn ordinary household objects into weapons. Ben also had this same problem as Splinter could plainly see.

However, Splinter could see that while the teenager had this obvious problem, he also had unlimited potential to become a great ninja warrior. So the human-turned-rat made a decision about how to truly unleash this unlimited potential that Ben possesses.

"You are wise to admit your own faults, Benjamin. A true warrior is not only a master of combat, but he is also a master of adaptability." Splinter said. "Which is why I have decided to train you in the art of ninjitsu."

"What? Really?!" Ben asked in surprise.

He certainly wasn't expecting to hear that from the humanoid rat. But Splinter merely smiled.

"You heard me! I shall start training you to become a Shinobi; a male ninja." Splinter explained.

This really threw Ben for a loop. He couldn't believe that he was finally going to be able to learn a new form of combat! Back when he was a Plumber, Ben always thought that he wouldn't need anything other than his Omnitrix in a fight. But now, he understood that there would be plenty of times where the Omnitrix would be rendered useless.

So Ben did something that he normally would never do. He got down on his knees, and bowed as low as he could to Splinter.

"Anata no masutāsupurintā. Saizen o tsukushimasu!" Ben said in Splinter's native language.

Splinter was genuinely impressed by Ben's knowledge of the Japanese language, let alone him actually speaking it perfectly. Nevertheless, Splinter entered "teacher mode" as he replied in a language he does not often use outside of training.

", Watashi no gakusei o jōshō." Splinter replied. "Anata no kunren wa kyō no shōgo ni kaishi sa remasu."

So Ben rose from his bowed posture, and left the dojo to prepare for his training. For he had a gut feeling that he would need this training sooner than he thought. And he would be right. For up on the surface world, Oroku Saki was preparing a plan to capture Karai, kill the turtles, and defeat Splinter.

A month has gone by since Ben started his ninjitsu training, and the boy seemed to be a natural at it! Donatello guessed that all those years of fighting aliens had something to do with it. However, Splinter was still very happy with the results of Ben's training.

The boy's muscles were beginning to fill out due to the rigorous physical conditioning, and Ben was also learning how to blend in with the shadows like a ninja should. He was even going through basic weapons training. Ben was currently going through the katas of a fighting style that Splinter thought would be good for him to learn.

It was a style known as the Fox Claw style. It revolves around quick movement and precise strikes at one's pressure points to defeat them. Ben seemed to be a natural at this fighting style, and it showed well.

"Yāme! That is enough for today, Ben. We will continue your training tomorrow." Splinter said.

"Hai, sensei." Ben replied with a bow.

Ben didn't know it at the time, but there would be many dark times ahead of him. But he would have a new family there to help him through it. As well as the one girl who would be able to heal his heart.

* * *

 _ ***Translations***_

 _ ***Thank you Master Splinter. I will do my best!***_

 _ ***Rise, my student. Your training begins at noon today.***_

 _ **I hope you guys enjoy this chapter, because I tried to make it a good one to show just how determined Ben is to become a good Shinobi! Don't forget to vote on the poll I posted. Next on my update list is Ben Tennyson's Five Nights at Frannie's.**_


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